


swimming lessons

by cherryconke



Category: Fire Emblem: Fuukasetsugetsu | Fire Emblem: Three Houses
Genre: Established Relationship, Explicit Sexual Content, Fishvain, Fishvain has two dicks, Human Felix, M/M, Mermaid Sylvain, Monsterfucking, Plot What Plot/Porn Without Plot, Praise Kink
Language: English
Status: Completed
Published: 2020-05-20
Updated: 2020-05-20
Packaged: 2021-03-02 23:34:55
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,615
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/24285184
Author URL: https://archiveofourown.org/users/cherryconke/pseuds/cherryconke
Summary: Sylvain teaches Felix how to swim.
Relationships: Felix Hugo Fraldarius/Sylvain Jose Gautier
Comments: 7
Kudos: 242





	swimming lessons

**Author's Note:**

> for [casey](https://twitter.com/eggyankee) – this fic takes place in her [wonderful](https://twitter.com/eggyankee/status/1261153673683623938/photo/1) [fishvain](https://twitter.com/eggyankee/status/1260808258740240385) [au](https://twitter.com/eggyankee/status/1258850886136336386)!
> 
> (for any subscribers: i deeply apologize if u were not expecting a monsterfucker fic to be sent to ur inbox. tbf, i was not expecting it either)
> 
> —
> 
> warning???: sylvain is Big. he has a tail + pseudo-human genitals (i.e. two dicks) in this fic. if that bothers u, pls don't read <3

“You’re doing great! Now just, uh, kick your legs– no, not in circles, kind of like you’re paddling, but with your feet...”

Sylvain’s tail rises up from the water, copper scales shimmering iridescent in the sunlight as he rolls it in a sinuous, smooth wave, practiced and perfect. Felix tries to mimic it with his own two legs, but only ends up clumsily splashing flecks of saltwater up into the air. He feels nowhere close to graceful, not next to his giant, half-shark of a boyfriend who’s been doing this for literal  _ centuries. _

“It’s not working,” he whines, kicking frantically against the pull of resistance, but his feet start to sink towards the depths, the weight of water threatening to drag the rest of his body down. His arms pinwheel out of instinct, struggling to keep afloat even though logistically he knows that the soft sand is only a few feet below and Sylvain is just a short distance away, a built-in boyfriend-buoy to cling onto if he grows too tired trying to tread water.

Sylvain brought him to the shallows today, hidden off the coast and away from the sharp, dangerous rocks that line the pier Felix meets him at each afternoon.  _ It’s about time you learned how to swim, love,  _ Sylvain explained as he carried Felix on his chest, his tail propelling them lazily through the colorful catamarans and modest fishing boats dotting the harbor. Felix had other plans in mind for today (namely, exploring all the ways his boyfriend’s wide, sharp mouth and tapered tongue could make him shake apart and forget everything save Sylvain’s name), but Sylvain had looked at him, so eager and earnest, a flash of love he couldn’t say no to.

The freedom of the open ocean gets to be too much when a particularly strong wave swells and drags him underwater, swift and relentless. His ears fill with Sylvain’s bubbly laughter as a large clawed hand plucks him out of the depths and back up into the air. Felix coughs, sputtering up a mouthful of seawater across Sylvain’s collarbone, legs splayed on either side of his broad chest.

“Gross,” Sylvain laughs, delighted. A thumb half the size of Felix’s entire face comes up to brush wet, tangled bangs from out of his face. Sylvain’s always so careful with him, even a whole year and a half-dozen scratches and scars later, earned from fumbling their way through an – unlikely – relationship together. Felix has learned a lot since then: how the fins framing Sylvain’s face where ears are on humans are incredibly sensitive for most merfolk; how one of Sylvain’s monstrous hands can fit the entirety of his waist within it; how Sylvain’s rumbled laughter warms him from the tips of his fingers to his pruned, numb toes.

He’s learned a lot – except how to swim.

“I’m useless at this,” Felix complains, wrapping his hand around Sylvain’s wrist, the other hooking around his neck for stability. Sylvain swims further out of the shallows, securing one of those massive hands around Felix’s waist as his tail sways and undulates in the water, easily keeping them both comfortable riding on the quiet, familiar swell of waves.

“You’ll get better with practice, my heart.”

Felix huffs. He knows Sylvain’s right, but spending what precious time they have together half-drowning doesn’t sound like his version of a fun date – no matter how patient Sylvain was, trying to teach him the basics of staying afloat.

“Just think, Fe,” Sylvain hums, a deep vibrato beneath Felix’s legs. He can’t help but shiver when a blunt claw tilts his chin up and forward, Sylvain’s pupils blown dark where he looks down at him. “All the places I can take you, once I’m sure you won’t drown.”

Felix scoffs, but he can’t hide the tremor that trails up his spine when Sylvain shifts him in his grip, moving him closer. A thick, warm tongue comes up to lick the dried salt from behind his ear, moving down to lap at the water in the hollow dip of his clavicle, and this time Felix groans, swaying atop Sylvain’s chest, fingers curling to find purchase in damp copper locks.

“There’s so much to show you,” Sylvain continues, like he isn’t trying – and succeeding – in taking Felix apart. A flattened palm comes up to cup the curve of his ass, a single finger rubbing damp friction there, the painful-pleasure pressure of his claws scratching shallow pink lines against his thighs drawing a quiet whine from Felix’s throat. 

“Or,” Felix pants, kissing a collar of bruises around the sundrenched freckles staining Sylvain’s shoulders, grinding unashamedly against his stomach, “we could just stay here.”

_ Forever,  _ his mind supplies, and it almost slips out, unbidden, but then Sylvain groans against him, dipping his massive head low to fit the wide circle of his pointed canines around his shoulder, teething light marks into the muscle there. Felix moans, a broken sound, already overwhelmed with the thought of being completely surrounded and filled. “I’m sure we could –  _ ah  _ – find s-something to do.” 

“Oh,  _ sweetheart,” _ Sylvain growls, surging up for a bruising, biting kiss. The smile he flashes at Felix is deadly, all sharp teeth and bright affection. “You’re gonna be the death of me.”

It’s a miracle they make it back to shore. Felix keeps distracting him, sucking a flurry of kisses into Sylvain’s collarbone, grinding back against the curve of his hand – but he somehow navigates them to land safely, keeping one hand anchored firmly around Felix’s waist. Sylvain plants his hands and hoists them both up onto a flat stretch of rock, sundrenched and smooth from years of rough scales rubbing against it, crooning soft reassurances all the while:  _ gonna make you feel so good, baby, gonna take care of you, fill you up.  _

Felix isn’t immune to it, the way Sylvain’s scarred muscles ripple beneath his thighs, the rusted copper shine of his hair in the golden summer sun, the glittering flash of crimson-orange scales reflecting saltwater skies. It’s intoxicating, the dangerous, otherworldly beauty of Sylvain, and sometimes Felix can’t believe that he’s actually  _ his _ to have like this, spread out and wanting beneath him. 

Sylvain’s face-fins flare when Felix peels off his shorts and tosses them somewhere up on the rocks, inching up the length of Sylvain’s body to position himself above the hot, velvet seam of his mouth. His hands wind through damp hair, and Sylvain keeps one hand anchored around his waist while the other traces careful pressure up and around his dripping cock, always mindful of his claws as they drag light marks across his belly.

“That’s it, baby, just like that…” Sylvain hums, obviously pleased when Felix finally sits back on his haunches and lowers himself down. He can’t help the broken  _ S-Sylvain  _ that slips out at the feeling of Sylvain’s tongue, warm and wet and  _ thick _ against the inside of his thighs. It’s always too much, being taken like this, wrapped up in damp, salty skin and scales just this side of too scratchy when he rubs his legs against them, searching for friction.

“Let me hear you,” he coaxes, licking unbearably close to his rim as Felix whines. The rumble of his voice sparks electricity up his spine, Felix feeling it more than actually hearing it, his warm pleasure barely audible over the waves hurling themselves against the rocky shoreline. Sylvain’s always so obsessed with the embarrassing noises he pulls from Felix’s chest, begging him to  _ use your words, my heart, I wanna hear how good I make you feel. _ The instinct to try and muffle his moans with the back of his arm is still there, though, clenching his teeth into sunburnt skin as Sylvain licks sloppy, wide laps of his tongue up and around his hole, sharp teeth grazing across the sensitive skin of his thighs. 

Felix hiccups back a moan, already overwhelmed. “C’mon. Need you inside, ’vain,” he pleads, looking down at the flash of brown eyes beneath him, hazy with amused affection and a hint of self-satisfied pride. His own cock is smearing precum and straining up against his stomach, but Sylvain completely neglects it in favor of pressing his thumbs into his hip bones, which are sure to leave a constellation scatter of dark bruises against his skin. Felix shifts, pressing one hand back against Sylvain’s chest, arching his back to make the angle easier on his jaw.

This is something they perfected early on, back when the thought of taking Sylvain’s cock inside his ass was laughable. Sylvain’s tongue is firm yet yielding, the perfect thickness to take Felix apart with just a few clever licks. Now, it’s the best way to open him up, Sylvain’s sharpened fingernails – claws, more like it – too sharp to be of any use; Felix’s fingers too small to make much of a difference. 

“Good kitten,” Sylvain murmurs, opening his mouth wide to teethe fleeting indents into Felix’s legs before adjusting his grip and pressing the tip of his tapered tongue against his hole. Felix can’t help but squirm against the intrusion as he pushes in slowly, speared open and gasping against the stretch. He’s started to practice at home, slicking his hand in oil and fingering himself open in a desperate attempt to recreate the feeling of Sylvain’s tongue licking deep inside him, or one of his cocks filling him up until there’s tears in his eyes. It’s never enough, but it helps to get used to the width, makes the transition from pain to pleasure easier. 

_ (I should get you a plug, angel,  _ Sylvain panted one time, deep inside of him,  _ keep you stuffed and full of my cum, would you like that?  _ The idea still plagues Felix’s lonely days and even lonelier nights.)

Pleasure comes over him in a slow, rolling rush as he relaxes into the wet warmth of Sylvain’s mouth, breath hot against his thighs. The wave of his orgasm threatens to drag him under, but Sylvain plucks him away before he has the chance to finish, lungs bellowing and arms shaking in exertion. 

“Easy, sweetheart, can’t have you coming too soon.” Sylvain grins, peppering his face with wide, wet, close-mouthed kisses. Felix shivers against him – he’s cool and damp despite the late-afternoon sun shimmering glittery heat on the waves.

“W-want you in me,” he manages to pant out, because if he’s learned anything over the past six months, it’s that Sylvain not only loves his noises, but his  _ words,  _ too, delighting whenever Felix whines and begs, showering him in praise whenever he starts a sentence with  _ I want  _ or  _ please. _

Predictably, Sylvain smiles, a dangerous curl of teeth flashing in the sunlight. “Anything for you, baby. You just gotta ask nicely.”

“I  _ am  _ asking nicely,” Felix grumbles, reaching around with one hand to grasp for the head of Sylvain’s cock, the other pressing up against his stomach to stabilize himself as he starts to inch backwards. Sylvain clicks his tongue, leaning down to pull Felix’s body back towards his face. Felix goes with – not like he has much of a choice, as struggling against Sylvain’s considerable, inhuman strength hasn’t ever proved effective before – but he pouts all the while, showing his clear displeasure at being denied.

“That doesn’t sound  _ nice  _ to me, Fe,” Sylvain teases, clearly amused, the fins flanking his face fluttering in laughter. Felix scowls, but before he can come up with something sarcastic, Sylvain readjusts him so that the wide, blunt head of his cock is pressing against his hole.

The logistics of fucking your two-dicked, half-shark boyfriend aren’t as tricky as Felix initially thought it might be. They’re limited in positions – thanks to Sylvain’s sheer width and size and not wanting to completely crush Felix beneath him – but they’ve managed to figure out a good, solid routine, one that always ends in Felix leaking cum and sore for days after, full and satisfied in a way he hadn’t known before Sylvain.

It starts with Sylvain flipping through the small drybag of Felix’s he’d set down on the rocks earlier. It’s the one he’s started carrying down to the docks, full of all the things he’s learned to keep with him after various trial-and-error dates with Sylvain: snacks and freshwater and sunscreen, but most importantly,  _ lube,  _ because Sylvain’s spit doesn’t exactly do the trick, and there’s no way in hell they’d get very far without it.

Sylvain fumbles, the bottle dwarfed in his hands as he coats one palm and drizzles the rest on Felix’s lower back. It’s warm, having spent time in the sundrenched bag, and slick where it slides between his cheeks. Sylvain curves a single finger there, continuing to tease as the head of one of his cocks presses into him. The other one rests off to the side, hard and leaking, twitching against Felix’s calf – Sylvain usually ignores it, choosing to devote all his attention to Felix, only starting to fist it against his back when he’s close.

There’s always a breaking point when Sylvain’s relentless teasing turns unbearable. For Felix, it’s usually around now, when he attempts to wriggle back and fuck himself on his cock but is held back by Sylvain’s steady grip around his waist. Whines rise from deep in his throat, throaty and needy and  _ wanting,  _ spilling out across the curved shell of Sylvain’s collarbone as Felix hangs his head. 

“C’mon, darling,” Sylvain nudges his chin up with his free hand, stroking a gentle knuckle across the curve of his cheek. “Use your words for me.”

_ “S–Sylvain,”  _ he says instead, fingernails carving crescent-moons around where he’s holding Sylvain’s forearms, aching to have all his thoughts wiped of anything but  _ full _ and  _ big  _ and  _ deep.  _ “P-please.”

“Yeah? Like this?” Sylvain feeds the tip of his cock into him with a smile, cradling Felix’s body carefully, like something precious. It’s dizzying, going from empty and loose to so, so full, stretched tight around the tapered, ridged head of his cock, gasping for air as Sylvain bends over him to kiss down his shoulders and up his cheeks, murmuring gentle praise the whole time, things like  _ just like that  _ and _ breathe, Fe, you’re doing so well, you were made for this, angel. Such a perfect fit, relax, relax, I’ve got you. _

Felix chokes out a sob as he pushes in, and in, and  _ in,  _ only to bottom out at the start of Sylvain’s thick, flared base. He feels like he can barely keep his eyes open, already exhausted from the heat of the sun and the stretch of Sylvain’s cock filling him up. He slumps against Sylvain’s chest, panting like he’s run a fucking marathon – this part has gotten easier and quicker over time, but it never fails to steal the breath from his lungs, to shock him with the sheer stretch. 

Sylvain waits, patient as ever, one hand spreading cupped palmfuls of cool water down his back, calming the heat-flush blooming across his chest as he tries to relax, falling boneless into the lulling pattern of his touch. He kisses Felix’s hands, and his face, and the top of his head. “Just like that, love. Relax for me. You feel so good.”

“F-fuck,” Felix hisses out, squirming around his cock, speared open and spread wide.  _ “Fuck,  _ s-so big.”

“You’re taking it so well, my heart. You’re so good for me,” Sylvain says. Here, like this, vulnerable and stripped bare, Felix wants so desperately to believe him. “I’m gonna move now, okay? You ready?”

Felix nods, his belly tight with want, stretched out and taut around Sylvain’s cock. Sylvain kisses him one last time, far too gentle for being balls-deep inside of him, and then –  _ then,  _ Felix proceeds to fall apart.

It’s always so good, the quiet, warm place his mind floats to in this much overwhelming pleasure, all raw nerves and electric energy beneath Sylvain’s touch. He barely registers the noises he’s making, hushed cries pressed into Sylvain’s bare chest, arms reaching up high to loop the tips of his fingers around his neck. Sylvain presses in, almost too slow, before pulling out again, starting up a careful, slow rhythm. Broad hands worship his body, roaming across his chest to thumb at his nipples, caressing the curve of his ass, digging a single claw into his thighs. It has Felix scrambling against his touch, crying out in broken moans as he fucks him slow and gentle.

“Look at you, baby,” Sylvain sighs into his ear. His hand comes around to graze over Felix’s stomach and the small yet noticeable bulge there whenever he thrusts all the way in. The pads of his fingers press down – careful, always careful – and Felix  _ wails,  _ tears tracking more salt down his cheeks. “Keep breathing for me,” he hums, continuing to massage himself through Felix’s belly. It’s– it’s so much, and somehow not enough at the same time.

Felix doesn’t really know what possesses him to whine  _ more, more,  _ but once he starts he can’t seem to stop. He writhes in Sylvain’s lap, far past the point of shame. 

“More? Baby, I can’t give you any more.” Sylvain taps on his cock again through the skin of Felix’s stomach, pausing his thrusts to nuzzle a kiss against his throat. “You’re already so full.” 

“F-fuck me like you mean it, then,” Felix sobs, cock-drunk and nearly delirious. He winds his hands into Sylvain’s hair, knuckles knotting in damp auburn. “Fuck me, please, please,  _ please–”  _

Sylvain’s laughter fills the air, genuine and rough-velvet, going straight to Felix’s dick. “Yeah? I’ll take care of you, sweetheart. I love when you ask so nicely.” He punctuates it with a brief kiss, before dragging Felix down, then up, repeating the process, each thrust growing harder and faster until every third one hits up inside of him perfectly. Each ridge of Sylvain’s thick, broad head caresses the spot that has him seeing white, stuttering broken fragments of  _ Sylvain  _ and  _ please,  _ torn between begging for it to stop and for Sylvain to stay forever and never leave, to live inside the hollow, fucked-out shell of his body. 

The hot, slick drag of Sylvain’s tongue across his neck is finally what does it, pushing him into rapid freefall as he comes, completely untouched, dripping across Sylvain’s belly and hips.

“Oh, there we go, sweetheart, just like that, you did so good–” Felix moans, his body gone limp from his orgasm and overstimulation, Sylvain still moving – slower, but steadier – inside him. Saltwater drips down his face as he presses himself into Sylvain’s chest, clinging on as Sylvain continues singing soft, delighted praise, until he, too, starts to shake apart, Felix clenching down around him, his hole milking his cock. This, too, was something he had to get used to – the messy stream of Sylvain’s cum leaking out of him after; that delicious, too-full feeling permeating long after he’s pulled out. Warm cum hits his back in thick spurts, Sylvain’s other cock rubbing friction between his cheeks as he moans and rides out his orgasm, teething a bruise into Felix’s neck.

He feels filthy, and fucked, and so  _ full  _ when Sylvain tips his jaw up into a soft, languid kiss, still deep inside him. Felix can already feel the trickle of cum down his thighs and the bruises starting to form around his ribcage and in the notches of his spine. 

“Easy, easy,” Sylvain hushes when he finally starts to squirm, the too-full feeling catching up to him all at once until Sylvain finally slips out, a small pool of cum following not long after. Felix whines, limbs sore as he curls up against Sylvain’s chest. He feels good, sleepy and satisfied like he usually does after sex, wishing they could stay here forever on the deserted shoreline, drunk on sunshine and saltwater and each other. Felix never stays long past sunset, not with the biting breezes and sometimes-storms that pass through in heavy thunderclouds and white-capped waves, but it’s during moments like these when he wishes he could. Nothing sounds better than luxuriating in Sylvain’s arms, safe and content, for the rest of the night.

He starts to doze almost immediately, the weight of Sylvain’s hand petting soothing circles in his back enough to put him straight to sleep, but Sylvain breaks the silence, cutting through the dreamy afterglow. “How are you feeling?”

Felix stretches, yawning while he tests his fingers and toes. He rolls out his wrists and ankles, shimmying up the front of Sylvain’s body to fit his forehead against his chin. “Good.”

There’s already a hint of delicious soreness in his joints – particularly his hips – but it’s nothing he isn’t used to already. Sylvain’s hands curl around his waist, and he’s content to be dragged along as he slips off the slate rock and back into the water. One hand keeps Felix afloat on his back while the other rinses the sweat and cum from his legs and back and belly, weightless silk touches soothing beneath the rolling surface of the water. When he’s finished, Sylvain flips onto his back, dragging Felix to rest against his chest.

“I love you, you know,” Sylvain murmurs, stroking damp hair off his forehead, propelling them in lazy, calming circles near the rocks. Water laps against Sylvain’s sides as he floats, and Felix hitches a leg over his hip to drag his foot in the small currents he’s making with his swirling figure-eights, comfortably content and bone-weary. The words light something deep and warm inside him, and he can’t help but lean further into Sylvain’s touch, fingers brushing careful delight down the sturdy line of his jaw.

“Yeah,” he hums against Sylvain’s mouth, pressing a slow kiss to the upturned corner. “I know.”

**Author's Note:**

> this started out as a drabble on [twitter](https://twitter.com/cherryconke) but then the brainworms got to me
> 
> apologies for any mistakes, this is unedited + written in a complete haze
> 
> ~~inspo for sylvain'd d*cks taken from the BD gunner lol~~


End file.
